1. Field of the Invention
This invention relates to an apparatus for holding a paper upon a platen drum of a video printer. In particular, this invention relates to a paper holding apparatus having two holding members mounted only on both ends of the platen drum, so that the apparatus allows a video printer to be able to print video signals on the paper fast by preventing a thermal head from making an random vertical up or down movement.
2. Description of the Background Art
In general, a video printer (in particular, a color video printer) uses a three-color ribbon in order to freely express or reproduce full colors of the video signal. The three-color ribbon is widely divided into a number first parts of having the components of Yellow, Magenta and Cyan and a number of second parts which have a separation strip for separating a set of the three-color components from an adjacent set of three color compounds.
A known color video printer which employs the three-color ribbon to print full colors of the video signal, should rotate the paper three times sequentially with the paper being held fixedly on the surface of the platen drum. A three-color ribbon is placed between the paper and the thermal head. In order to freely express the entire gradations of the colors, the video printer should precisely control the thermal sublimation (radiation). In this way of reproducing the video signal, there is a need for the paper to be rotated once placed fixedly on the platen drum of the video printer. For this purpose, the video printer generally requires a paper holding apparatus.
As illustrated in FIG. 1, a video printer having such a conventional paper holding apparatus therefor is presented. This video printer includes a platen drum 52 for rotating a paper 51, a paper holding apparatus for fixedly holding the paper 51 on the surface of the platen drum 52, a color ribbon 61, a ribbon cartridge 60 and a thermal head 54 for controlling the thermal sublimation of the color ribbon 61.
Referring to FIG. 3, there is shown a cross sectional view along the line A--A' of FIG. 1, taken when the paper holding apparatus 53 passes through and under the thermal head 54. As generally understood, the thermal head 54 should rise periodically in order to avoid collision with the paper holding apparatus 53 while printing the video signals. In other words, the paper 51 which is fixedly held on the surface of the platen drum 52 by means of the paper holding apparatus 53 will be rotated three times sequentially so as to reproduce a complete sheet of a video image. In this case, for every rotational period of the platen drum 52 the thermal head 54 should make movement. Therefore, it is a significant problem of the conventional paper holding apparatus is that the video printer takes a relatively long printing time. This is because of the vertical movement of the thermal head 54 and that the video printer requires a control circuit for controlling the vertical movement and a control mechanism. The precision of printing video signal may also be reduced undesirably because of the vertical movement.
The length of the color ribbon 61 must be increased to an extent that corresponds to the time required for the paper holding apparatus to pass through and under the thermal head 54. Therefore for the conventional video printer causes an undesirable waste of the color ribbon.